Unfortunately that whitepaper says nothing on how they do it. My theory is that they're using the Dynect CDN manager. This is a tool created by Dyn to let comp

Unfortunately that whitepaper says nothing on how they do it. My theory is that they're using the Dynect CDN manager. This is a tool created by Dyn to let companies use their DNS system to pick which CDNs are used where, and to create round robin rules that are percentage and region based. I confirmed this by checking their nameservers, which are currently pointed at Dyn (ie, NS1.P24.DYNECT.NET). The thing that amuses me about this is that Edgecast offers this same service at a far, far more reasonable price. I'm not sure why they didn't just use them.